1. Field of the Invention
This invention relates to a thermoplastic dental impression tray that may be shaped to conform to a patient's dental arch.
2. Description of the Related Art
Dental impression trays are used to hold impression material for making a model of a patient's oral cavity so that a crown, bridge, denture, restoration or the like can be made. To make the model, a quantity of impression material is placed in an open trough or channel of the tray, and the tray is then pressed onto the dental arch to make a female cast of the desired area of interest. The cured impression is then used to form a male model which replicates the selected area of the patient's arch.
Recently, there has been increased interest in the use of thermoplastic impression trays which may be heated and then shaped to closely conform to the patient's dental anatomy. Since dimensions of the dental arch may vary widely from patient to patient, such trays may be molded when heated to adjust the height and width of the channel of the tray to accommodate the selected area of the patient's. arch In this manner, the tray may be shaped to conform to the arch so that an accurate impression may be made, while enabling the relatively expensive impression material to fully surround the selected area of the arch without wastage. Examples of such moldable impression trays are described in U.S. Pat. Nos. 4,227,877, 4,361,528 and 4,657,509.
The height and width of the channel of known moldable impression trays may be expanded only to certain practical limits. For example, if the height of the channel is enlarged beyond a certain dimension as the tray is molded, the width of the channel may decrease to a dimension too small to accommodate the width of the arch. On the other hand, decreasing the height of the channel when molding the tray may increase the width of the channel to a dimension much greater than needed, such that a certain amount of the impression material is wasted. Another problem is encountered when the patient's arch is longer than average and cannot be accommodated by the tray at hand.
The aforementioned U.S. Pat. No. 4,227,877 illustrates a moldable maxillary impression tray having a U-shaped trough that is connected to a central section for engaging the vault of the patient's palate. The vault engaging section includes a central pleat extending in the sagittal plane, and the pleat allows lateral adjustment of the distance between the two posterior end portions of the trough when the tray is heated, so that central vault section of the tray may be adjusted to compensate for the concavity of the palatal region of the individual patient. However, such construction does not satisfactorily overcome the problem of readily conforming the height, width or length of the trough to accommodate the configuration of the patient's dental arch.